by henk21cm » Sat Jun 14, 2008 11:04 am
http://antwrp.gsfc.nasa.gov/apod/image/ ... ndlerM.jpg
The NGC5195 is
believed to slide by, behind the NGC5194. An observation that supports this hypothesis is the amount of asymmetry in 94.
A simple test, you, every day reader of the APOD, can do at home, is fetch an overhead sheet. If you don't have such a sheet, -like me- use one of these transparent plastic bags which encase magazines, sent to you via snail mail. Press it flat on your monitor and draw the contours of the two spiral arms of 94 on this bag, with a felt tip pen! Mark carefully the center of the galaxy. Then rotate the plastic bag by 180 degrees around the galaxy center, until the drawn lines cover roughly the opposite spiral arms. The difference between the drawn lines and the actual spiral arms is a measure for the amount of asymmetry. I suppose that professional astronomers will use image processing techniques and express the amount of asymmetry into a number. We amateurs use an effective low tech solution.
Nevertheless in the lines drawn I did not notice a lot of asymmetry, so the distance between 94 and 95 must be large compared to the length scale of 94. This supports the hypothesis. Why?
Suppose 95 is in the same plane as 94. Then, the distance between the right spiral arm and 95 would have been 3 times smaller than the distance between the left spiral arm and 95. Expressed into attractive forces, it is nearly an order of magnitude. The asymmetry would have been considerable. This is in sharp contrast with the observation, so the assumption: "95 is in the same plane as 94" is not correct.
In spite of all theoretical aspects, which focus the attention to details and numbers, i DO appreciate M51 for its magnificent appearence. My favourite!
[url]http://antwrp.gsfc.nasa.gov/apod/image/0806/M51HST-GendlerM.jpg[/url]
The NGC5195 is [url=http://hubblesite.org/newscenter/archive/releases/2005/12/image/a]believed to slide by, behind the NGC5194[/url]. An observation that supports this hypothesis is the amount of asymmetry in 94.
A simple test, you, every day reader of the APOD, can do at home, is fetch an overhead sheet. If you don't have such a sheet, -like me- use one of these transparent plastic bags which encase magazines, sent to you via snail mail. Press it flat on your monitor and draw the contours of the two spiral arms of 94 on this bag, with a felt tip pen! Mark carefully the center of the galaxy. Then rotate the plastic bag by 180 degrees around the galaxy center, until the drawn lines cover roughly the opposite spiral arms. The difference between the drawn lines and the actual spiral arms is a measure for the amount of asymmetry. I suppose that professional astronomers will use image processing techniques and express the amount of asymmetry into a number. We amateurs use an effective low tech solution.
Nevertheless in the lines drawn I did not notice a lot of asymmetry, so the distance between 94 and 95 must be large compared to the length scale of 94. This supports the hypothesis. Why?
Suppose 95 is in the same plane as 94. Then, the distance between the right spiral arm and 95 would have been 3 times smaller than the distance between the left spiral arm and 95. Expressed into attractive forces, it is nearly an order of magnitude. The asymmetry would have been considerable. This is in sharp contrast with the observation, so the assumption: "95 is in the same plane as 94" is not correct.
In spite of all theoretical aspects, which focus the attention to details and numbers, i DO appreciate M51 for its magnificent appearence. My favourite!